Advances in photocatalytic degradation of organic pollutants in wastewaters: harnessing the power of phthalocyanines and phthalocyanine-containing materials

Access to clean water is increasingly challenging worldwide due to human activities and climate change. Wastewater treatment and utilization offer a promising solution by reducing the reliance on pure underground water. However, it is crucial to develop efficient and sustainable methods for wastewater purification. Among the emerging wastewater treatment strategies, photocatalysis has gained significant attention for decomposing organic pollutants in water, especially when combined with sunlight and a recoverable photocatalyst. Heterogeneous photocatalysts have distinct advantages, as they can be recovered and reused without significant loss of activity over multiple cycles. Phthalocyanine dyes, with their exceptional photophysical properties, are particularly valuable for homogeneous and heterogeneous photocatalysis. By immobilizing these photosensitizers in various supports, hybrid materials extend their light absorption into the visible spectrum, complementing most supports' limited UV light absorption. The novelty and research importance of this review stems from its discussion of the multifaceted approach to treating contaminated wastewater with phthalocyanines and materials containing phthalocyanines. It highlights key aspects of each study, including photocatalytic efficiency, recyclability characteristics, investigation of the generation of oxygen species responsible for degradation, identification of the major degradation byproducts for each pollutant, and others. Moreover, the review includes tables that illustrate and compare the various phthalocyanines and supporting materials employed in each study for pollutant degradation. Additionally, almost all photocatalysts mentioned in this review could degrade at least 5% of the pollutant, and more than 50 photocatalysts showed photocatalytic rates above 50%. When immobilized in some support, the synergistic effect of the phthalocyanine was visible in the photocatalytic rate of the studied pollutant. However, when performing these types of works, it is necessary to understand the degradation products of each pollutant and their relative toxicities. Along with this, recyclability and stability studies are also necessary. Despite the good results presented in this review, some of the works lack those studies. Moreover, none of the works mentions any study in wastewater.


Introduction
Clean water is an essential requirement for human health.The principal drinking water sources include groundwater, lakes, canals, rainwater, and sea water. 1,2Recently, there has been a concern worldwide about providing sustainable, pure water due to the continuous increase in consumption, population growth, and industrial activity. 3,4The demand for freshwater resources for domestic or industrial use has led to scarcity. 3,5is demand is expected to increase by nearly one-third in 2050, according to the United Nations' World Water Development Report 2018. 6Therefore, to meet the increased water requirement, the scientic community is developing efficient wastewater treatment methods. 7Conventional wastewater treatments consist of a combination of physical, chemical, and biological processes to remove organic matter and, in some cases, inorganic nutrients. 8The methods for water purication are divided into six processes: adsorption, biotechnological, magnetic, membrane, and (photo)catalytic. 1 Concerning the photocatalytic processes, the disadvantages of the 'traditional' homogenous photocatalysts, namely their recovery and reuse, were overcome by the advent of heterogeneous photocatalysts and allowed the implementation of large-scale photocatalytic transformations.However, homogenous photocatalysts are still useful for nding potentially promising molecules for heterogeneous photocatalysis. 9,10n the past decade, nanomaterials such as SiO 2 , ZnWO 4 , ZnO, brous materials, ferritic nanomaterials, and carbonbased and TiO 2 nanomaterials have been reported in UVvisible light photocatalysis. 7,11Among them, the most studied and used are the TiO 2 nanomaterials, discovered over three decades ago.They showed great photocatalytic activity, hydrophobicity, long-term stability, lower toxicity and costs (compared with other nanomaterials), and self-cleaning ability. 9,10To apply heterogeneous photocatalysis to wastewater treatment, the cost of the process should be minimal.Thus, recyclability presents a vital feature for a photocatalyst. 10,12here is an urge to nd alternatives to improve the photocatalytic performance of materials frequently used as photocatalysts.For example, some materials only absorb UV light, representing ca. 5% of the solar spectrum.For example, modifying these materials with dyes can improve their photocatalytic efficiency under solar light. 10,13In fact, the sensitization of the photocatalyst induces faster destruction of the organic pollutants during the photocatalytic activity. 7,10,14hthalocyanines (Pcs) are dyes that can be photoactivated by visible light to promote the degradation of organic materials. 15][17][18][19] Usually, the synthesis of a phthalocyanine from a monosubstituted phthalonitrile affords a mixture of regioisomers due to the variation of the peripheral position of the R groups (Fig. 1).Similarly, the tetramerization of a non-symmetrical disubstituted phthalonitrile (R 1 s R 2 ) also gives a mixture of regioisomeric phthalocyanines.Given that, in this paper there are symmetrical and non-symmetrical tetra-and octasubstituted phthalocyanines with various regioisomers that are represented by the condensed structural formulae notation "Formula type I ′′ and "Formula type II" (Fig. 1).So, the type I notation, despite not being formal, is oen preferred to type II due to its high level of clarity, and it will be used in this review when needed.
This review focuses on the photocatalytic degradation of organic pollutants typically found in wastewater by using several phthalocyanines as catalysts.There are several highly cited reviews in photocatalysis, 15,32,33 but an up-to-date review is needed.A comprehensive review of the published works in this eld during the last 17 years is presented herein.The pollutants mentioned in this review are divided into ve main sections: phenol and phenol derivatives, organic dyes, agrochemicals, pharmaceuticals, and other pollutants.The novelty and research signicance of this review are based on mentioning the multidisciplinary treatment of pollutant wastewater using phthalocyanines and phthalocyanine-containing materials, evidencing the main details of each work when these parameters are determined and provided in the multidisciplinary reports, such as the: (i) photocatalytic rates, (ii) recyclability properties, (iii) study of the main generated oxygen species responsible for the degradation, (iv) the main degradation products of each pollutant, and (v) among others.However, there is a lack of some of these parameters in several reports.In this review, it is also provided some tables to show and compare the different phthalocyanines and supports used in each work for pollutant degradation.At the end of the review, some key insights and future perspectives will be presented to inspire future research.

Mechanism of the photocatalytic degradation of organic pollutants
Among the various methods to remove the organic pollutants in wastewater, photooxidation is the most used.It involves the in situ generation of reactive oxygen species (ROS) that react with the pollutants, leading to their oxidation and, preferably, decomposition. 31nder visible light irradiation, (metallo)phthalocyanines (MPc, M = 2H or metal ion) in a support system are excited and transfer electrons to the conduction band of the support (Fig. 2).The conduction band mediates the electron ow from the MPc to the electron acceptors on the support.It is important to highlight that the electron transfer between MPc and the conduction band of the support must be faster than the relaxation to the ground state. 7,34On the other hand, the excited phthalocyanine (MPc*) can act as a sensitizing oxidant (reacting directly with the pollutant) or transfer its energy to molecular oxygen to form ROS.6][37] In some studies, H 2 O 2 is used to increase the amount of OHc and, thus, enhance the photocatalytic activity. 14,31,38The nal step in the photocatalytic reaction is the relaxation of the photocatalyst to the ground state; a new catalytic cycle is then started. 7,9,10,14,33In the case of solar irradiation, UV light can also excite the support, increasing the formation of ROS. 7

Photocatalytic degradation of organic pollutants
Water contaminants such as phenolic compounds, dyes, agrochemicals, pharmaceuticals, etc., are hazardous to humans and harmful to the environment.Many of these substances are resistant to natural degradation processes.These contaminants reach natural waters through domestic and industrial activities in a continuous way, and that is attracting global concern.Even in localised contaminant sources, like industrial effluents, their elimination by conventional methods (chemical precipitation, ltration, electro-deposition, ion-exchange adsorption, and membrane systems) can be either slow or difficult. 39For the organic contaminants, photooxidation is a promising alternative to those methods.
Due to structural differences, each contaminant type raises specic degradation problems.Therefore, the results concerning the photooxidation/degradation of organic pollutants are discussed here by contaminant families, aiming to highlight the successes and drawbacks of the method for each contaminant type.It is important to mention that complete mineralization of the pollutants should be achieved in an appropriate period.The conversion of a pollutant into another compound, which could also be toxic, should be avoided. 40Therefore, each pollutant's degradation should be studied to evaluate if complete mineralization was achieved.Unfortunately, the degradation products of the pollutants are not mentioned in many of the studies of published articles.Moreover, many published works also do not mention recyclability studies.The recyclability of the composites used as photocatalysts is also essential when considering their viability in water and wastewater treatment. 41

Phenol and phenol derivatives
The rst family of contaminants to be discussed is the phenolic compounds.These are aromatic compounds with one or more hydroxyl groups linked to the aromatic ring(s).These compounds are found in the wastewater of several industries like petroleum reneries, chemical synthesis, plastics, dyes, detergents, and textiles. 42The appearance of phenolic compounds could also arise in the aquatic environment from natural sources, namely through algal secretion, hydrolysable tannins, and avonoids.However, the most hazardous ones are phenol derivatives like chlorophenols, nitrophenols, bisphenol A (BPA), naphthol, catechol, etc. 39 The presence of phenolic pollutants and their metabolites in living cells can cause mutagenicity, carcinogenicity, and endocrine-disrupting chemicals.
For this reason, they are considered human health and environmental hazards. 43The elimination of these derivatives is sometimes incomplete, so nding promising alternatives for its removal from wastewater becomes essential.The following sections will mention the degradation of these pollutants using several phthalocyanines.Also, in the following sections, studies regarding the degradation of chlorophenols using several phthalocyanines will be reported.
3.1.1.Phenol.Phenol is an organic aromatic compound with a hydroxyl group linked to a phenyl ring.This can exist in the environment either naturally or chemically.In Nature, it appears as a part of coal and creosote, decomposing organic materials, and a by-product of plant metabolism.Chemically, it can be produced through the oxidation process of toluene.The presence of a high concentration of phenol in wastewater can lead to a carcinogenic problem.It can also lead to chlorine in water and form chlorophenols, which are also toxic to organisms. 44For this reason, it becomes important to study its elimination.So, Iliev and co-workers 45 studied the photodegradation of phenol in water under visible light irradiation (l > 400 nm) using Zn(II), Co(II), and Al(III) mononuclear phthalocyanines and the water-soluble polynuclear metallophthalocyanine complexes Zn1 and Al1 (Fig. 3).In an alkaline medium (pH = 13), achieving the best degradation rate was possible using the Zn1 (r = 128.80min −1 ).The activity of this catalyst could be increased to r = 152.44min −1 by adding bulky cations, like tetrabutylammonium, that decrease the aggregation of the polynuclear Zn1 and, consequently, increase the 1 O 2 quantum yield (Table 1).
Under the same conditions, the phenol degradation rate was lower using the mononuclear Zn2 (Fig. 4) (r = 27.0 min −1 ). 45hen compared with Al2Cl (Fig. 4) (r = 17.13 min −1 ), the Al1Cl and Co1 (Fig. 3) exhibited higher photocatalytic activities (r = 39.21 and 0.12 min −1 , respectively).The authors conrmed that 1 O 2 is the main ROS involved in the degradation process of phenol.The oxidation product, 1,4-benzoquinone, could be further degraded into fumarate and maleate at an alkaline pH (pH = 13, Fig. 5).No assays regarding the recyclability and photostability of the photocatalyst were performed in this study.
Wu, Xing, and co-workers 46 studied the photodegradation efficiency of phenol in water (at different pH) under visible light irradiation in the presence of H 2 O 2 , using Pd3 (Fig. 4) immobilized on a mesopolymer (Table 1).The photodegradation rate could achieve 61% and 69% at acidic and neutral pH values within 420 min.On the other hand, there was 98% phenol degradation at alkaline pH aer 360 min.Also, H 2 O 2 was essential for the photocatalytic process as it increased from 56% to 98% under the same conditions when H 2 O 2 was added.Aer four cycles, the photodegradation of phenol remains unchanged using Pd1-FDU-15.The degradation products are the same as reported before. 45u and co-workers 47 and Iliev and co-workers 48 studied the photooxidation of phenol using TiO 2 modied with Al3 and H 2 4 (Fig. 4) in aqueous media under visible light irradiation (l > 400 nm).The rst authors compared the photooxidation rates with that obtained with H 2 4 immobilized on Al 2 O 3 .This rate was obtained by measuring the amount of CO 2 produced at the end of the catalytic process.When using H 2 4-TiO 2 (1.50 mol CO 2 / mol substrate), the photooxidation rate is much higher than H 2 4-Al 2 O 3 (0.95 mol CO 2 per mol substrate).The second authors could efficiently degrade phenol (∼90%) within 590 min with an optimum amount of Al1 (Table 1) loaded on a TiO 2 (1.0 wt%).Concerning the main ROS involved in the photodegradation process, Iliev 48 reported O 2 c − and HOOc, which could lead to the same products reported before by these authors. 45Xu and co-workers 47 identied the same ROS as Iliev 48 but did not report the degradation products.None of these works mentioned the photostability studies of photocatalysts.
Yang and co-workers 49 studied the photodegradation of phenol in aqueous media under visible light irradiation (l $ 420 nm) in the presence of H 2 O 2 (Table 1) and using Fe4 (Fig. 4) Fig. 3 Polynuclear phthalocyanine complexes M1.
immobilized on graphene nanosheets (Fe4/GR) as the photocatalyst.According to the authors, the p-p stacking interaction between Fe4 and graphene (GR) forms a donor-acceptor system.The loading of Fe4 promotes the exfoliation of the graphene sheets and enables the dispersion of Fe4 on graphene.As expected, the introduction of Fe4 into the GR greatly enhanced the photocatalytic activity of the composites since the p-p interactions between the planar aromatic GR and Fe4 enable the electron transfer from the donor (Pc) to the acceptor (support).Within 180 min of irradiation, the GR/Fe4-0.25 (25 wt%) could achieve a photocatalytic rate of 77%, compared with Fe4/Al 2 O 3 and Fe4/CNT, which were unable to degrade phenol.For the other materials used, such as Al 2 O 3, the donor-acceptor system does not occur.The Fe4/GR could be reused up to 4 times without signicant loss of activity (10%).In this study, the authors analysed the mechanism involved in forming the ROS (O 2 c − , HOOc, and cOH) but did not identify the main degradation products nor the stability and photostability of the used materials.
Xu and co-workers 50 studied the photodegradation of phenol under visible light irradiation (l > 450 nm) using AlCl4, Cu4,  which will be discussed later.Moreover, the photooxidation rate of phenol suffers a gradual loss of activity aer 4 cycles of the experiment using AlCl4.This loss of activity might be due to the degradation of the surfactant by the generated singlet oxygen or by the reduction of the sorption process that seems essential for the degradation process.
3.1.2.4-Methylphenol (p-cresol).4-Methylphenol or pcresol has been shown to cause uremia (retention of solutes by healthy kidneys).This molecule is part of the protein-bound uremic toxin milieu.The toxicological effects of p-cresol are related to its metabolism end products. 111,112It is highly resistant to natural degradation and can persist in the environment.This persistence and its harmful characteristics require a specic treatment given that the current methods have serious drawbacks like extreme operating conditions and the generation of harmful intermediates.Given all of this, it is necessary to nd new alternatives to degrade this pollutant. 113DU is a hexagonal mesoporous material, and this type of mesopolymer material has high physicochemical stability (despite the pH variation of the solution) and can adsorb phenolic pollutants from wastewater through p-p interactions and hydrogen bonding. 114,115So, Xing and co-workers 51 studied the photocatalytic degradation of 4-methylphenol under visible light irradiation by using a palladium phthalocyanine Pd3 (Fig. 4) graphed through p-p interactions onto the FDU-14 mesopolymer (FDU-14-Pd3).Aer 180 min in basic conditions and with H 2 O 2 , it was possible to achieve 97% degradation of 4methylphenol.Only 76% and 79% degradation rates were achieved in acidic and neutral conditions, respectively.This can be explained by the fact that 4-methylphenol must be deprotonated to 4-methylphenolate, which is more susceptible to oxidizing agents.Adding H 2 O 2 to the photocatalytic system improved the degradation rate from ca. 40% to 97% aer 180 min of light irradiation.In the dark, there is no degradation of 4-methylphenol.The degradation rate of 4-methylphenol remained unchanged aer the experiment four times using the FDU-14-Pd3 photocatalyst.Similar photooxidation rates of 4methylphenol were obtained using Pd3-FDU-15.
3.1.3.4-Nitrophenol.4-Nitrophenol (4-NP) is widely used in synthesising pesticides, drugs, and dyes in industries that release it into the environment.Acute exposure to 4-NP leads to liver and kidney damage, cancer, and systemic poisoning.In case of direct discharge in wastewater, it can endanger public health. 116,117So, developing new methods to eliminate this threat.
Nyokong and co-workers 52,84,97,118 reported the photodegradation of 4-NP in aqueous or organic media in the presence of a large diversity of phthalocyanines.In a rst study, 52 the water-soluble octacarboxy Zn18 (Fig. 6) and a mixture of mono-, di-, tri-, and tetra-sulfonated zinc(II) phthalocyanines (ZnPcS mix ) were used as photocatalysts, and the experiments were carried out in aqueous solutions at pH = 8.2.The authors concluded that the quantum yields of 4-NP degradation were closely correlated with the singlet oxygen quantum yields (F D ) and the phthalocyanines' aggregation (Table 2).Zn18 showed the highest F D (F 4NP = 6.5 × 10 −3 and 29% aggregation) followed by ZnPcS mix (F 4NP = 7.9 × 10 −4 and 49% aggregation) and the Zn3 (F 4NP = 1.5 × 10 −4 and 78% aggregation). 52However, in this study, the most effective catalyst was ZnPcSmix since Zn18 degrades readily during catalysis.The products of the photodegradation of 4-NP were identied as hydroquinone and 4nitrobenzene-1,2-diol.
According to the authors, the PAA polymer bres were unsuitable for application in aqueous media due to their extensive solubility that induces a gelatinous solution.No photocatalytic degradation of any pollutants occurred even aer 720 min of irradiation using the covalently linked Lu11OAc-PUR bres.The same occurred for the bres where Lu11OAc and PUR were mixed.These results contrast those reported for Lu29OAc and Lu7Oac, which are very photoactive materials. 97,122he absence of photocatalytic activity can be related to the morphology of the bres because they are not porous enough for sufficient interaction between the reactive species and the photoactive phthalocyanines.
The PS and PSU polymer bres are insoluble in water and suitable for photocatalytic degradation assays.There was a 40% degradation of 4-NP under visible light irradiation (l > 400 nm) aer 150 min of irradiation when using Lu7OAc/PS, Lu8OAc/PS, Lu12OAc/PS, and Lu29OAc/PS (Table 2).It was possible to obtain a better photocatalytic degradation rate when using the unquaternized Zn8/PS bres compared to the quaternized Zn12/PS bres.The 4-NP could be degraded more efficiently using the peripherally substituted Zn7/PS bres compared to their non-peripheral analogue (Lu29/PS).The photooxidation rate of 4-NP could be maintained even aer the photocatalyst was reused up to three times.Regarding the stability of these catalysts, the author only mentioned that the PSU functionalized with metal phthalocyanines was relatively stable under the same light intensity as in the photocatalytic studies.It is important to mention that aer the rst cycle of the reusability studies when dried, these bres folded up, forming a hard lump, and could not be applied again.The 1,4-benzoquinone and hydroquinone were identied as the major products of the 4-NP degradation.
In another study, 118 they studied the degradation of 4-NP in aqueous media under visible light irradiation (l = 400-600 nm) using composites based on the adsorption of several palladium(II) phthalocyanines 19-23 (Fig. 6) and 26-28 (Fig. 6) in singlewalled carbon nanotubes (SWCNTs, Table 2).In basic media (pH = 8.5), the photocatalytic rate using all composites follows   ).It was possible to obtain a better photodegradation of 4-NP for the composites bearing long alkyl chains.There was no signicant loss of degradation rate of 4-NP (∼7%) aer three cycles of the experiment.This study identied 1,4-benzoquinone, hydroquinone, and 4nitrobenzene-1,2-diol as the major products of the degradation process.All photocatalysts proved to be stable for 400 min.
Palmisano and co-workers 120 studied the degradation of 4-NP in aqueous media using H 2 13 and Cu13 (Fig. 4) immobilized in polycrystalline TiO 2 samples and investigated their photocatalytic behaviour in the degradation of (Table 2).The Fig. 7 Lu(III)29OAc a-substituted phthalocyanine complex used by Nyokong and co-workers. 84,97,121hotocatalysts remained stable for 420 min under irradiation.
Complete degradation of 4-NP was observed aer 60 min irradiation with UV light and using 1% or 1.5% Cu13/TiO 2 .On the other hand, there was only 50% degradation aer 60 min irradiation (but complete degradation aer 5 h) when using H 2 13/ TiO 2 .Compared with bare TiO 2 (86% degradation), only Cu13/ TiO 2 showed enhanced photocatalytic activity.Xu and co-workers 50 accessed the degradation of 4-NP in an aqueous medium at pH 11.2 under visible light irradiation (l > 450 nm) using Al4Cl (Fig. 4) inserted into modied bentonite (with the surfactant cetyltrimethylammonium bromide) (Table 2).It was possible to achieve 73% degradation of 4-NP aer 290 min of irradiation.For this pollutant, no degradation products were identied.
3.1.4.4-Chlorophenol.4-CP belongs to a group of toxic environmental pollutants that must be eliminated.Some conventional treatments like chlorination and adsorption currently perform their removal.However, they have some drawbacks, like requiring longer treatment to break down organic pollutants or generating carcinogenic by-products.Thus, photocatalysis is a promising alternative. 123Xu and coworkers 50 could achieve 71% degradation of 4-CP under visible light irradiation (l > 450 nm) in aqueous media using Al4Cl (Fig. 4) inserted into modied bentonite (Table 3).
In another study, the authors 98 observed that a higher degradation rate constant of 4-NP was obtained using In31Cl/PS (t 1/2 = 182.0min) bre followed by In9Cl/PS (t 1/2 = 217.0min) and In30Cl/PS (t 1/2 = 866.0min) -Table 3. The high activity of In31Cl/PS could be due to the high singlet oxygen generation values (F D = 0.50) and the high surface area of their bres.The number of charges did not seem to inuence the photocatalytic activity of the conjugates since In9Cl/PS has more charges than In31Cl/PS and lower photocatalytic activity.
Regarding gold nanoparticles, 101 high degradation rate constants and low lifetimes were observed for the Zn14-AuNPs/ PS bres (Fig. 4 and Table 3).Also, it was possible to achieve higher degradation rates when coupling AuNPs.In a study with Amberlite, Nyokong and co-workers 54 observed that the composite degraded ∼70% of 4-CP aer 30 min of irradiation.Regarding this pollutant, no degradation products were iden-tied.The authors extended the photocatalytic study to 2,4-CP, 2,4,6-TCP, and pentachlorophenol (PCP).Moreover, the study was extended to other metallated phthalocyanines for this last organic pollutant.Regarding carbon materials, Nyokong and co-workers 110 compared the degradation efficiencies of 4-CP when using Pd19/SWCNTs and Pd26 in aqueous media under visible light irradiation (Fig. 6 and Table 3).Pure Pd26 exhibited higher photocatalytic activity (91% for 4-CP) than the hybrid material (42% for 4-CP).The Pd26/SWCNTs catalyst cannot be reused without signicant activity loss.Despite the low photocatalytic rates of the Pd26/SWCNTs hybrid, Pd26 had excellent photocatalytic activity and may be applied in homogenous photocatalysis.Chen, Lu and co-workers 55 studied the photooxidation of 4-CP in aqueous media under visible light (l > 400 nm) using visible light-responsive photocatalysts based on g-C 3 N 4 and polyacrylonitrile (PAN)-supported g-C 3 N 4 coupled with zinc(II) phthalocyanine 2 (g-C 3 N 4 /Zn2and g-C 3 N 4 /Zn2/PAN, Fig. 4. Zn2 was covalently bonded to g-C 3 N 4 through the carboxy group of the MPc and an amine of g-C 3 N 4 (to form an amide).Aer 90 min of visible light irradiation, ∼98% of 4-CP was degraded by this photocatalyst, which is higher when compared with bare g-C 3 N 4 and Zn2 (Table 3).These results are due to the synergistic effect between g-C 3 N 4 and Zn2.More importantly, the photocatalytic degradation of 4-CP was as high as 99% aer  ten cycles, with no decrease, indicating that the catalyst has broad application for removing organics in polluted waters.The authors did not report the degradation products nor the stability of the photosensitizers under irradiation. 55n a new report, 56 the authors studied the photooxidation of 4-CP using g-C 3 N 4 /Zn2 (Fig. 4) as the catalytic entity, and PAN nanobers were employed as support to overcome the shortcomings of easy aggregation and to enable an easy recycling process.In the visible light studies, the removal rate of 4-CP using g-C 3 N 4 /Zn2/PAN as photocatalyst was higher than with g-C 3 N 4 /PAN, reaching a maximum of ∼98% aer 270 min of irradiation (Table 3).The g-C 3 N 4 /Zn2/PAN was reused up to ve times without signicant loss of activity.In both cases, the authors did not refer to the stability of the catalysts (effect of photobleaching) under irradiation nor the degradation products of 4-CP.
Several studies were performed regarding the degradation of 4-CP with MPcs supported on TiO 2 .For example, Xu and coworkers 47 evaluated the photocatalytic ability of Al2 (Fig. 4 adsorbed on TiO 2 and could achieve a complete degradation aer 420 min of visible light irradiation with an optimum amount of Al2 loaded on TiO 2 of 1.0 wt% (Table 3).Also, the authors could perform four photocatalytic cycles with a decrease of 40% in the photodegradation rate, which can be due to the photobleaching of Al2 during the photocatalytic assay.1,4-Benzoquinone, hydroquinone, formic and acetic acid were identied as the degradation products of 4-CP.
Pirbazari and co-workers 57,58 studied the photocatalytic activity, in aqueous media, of 4-CP by using Co(II)3 immobilized on TiO 2 nanoparticles.In both studies, 57,58 aer 90 min under visible light irradiation (l > 400 nm), it was possible to degrade 50% of 4-CP with Co3-TiO 2 , which could be increased to ∼100% in the presence of H 2 O 2 (Table 3).These results are auspicious; however, recyclability studies are crucial to determine the potential use of this photocatalyst in wastewater treatment.In this sense, in the second study, 58 a decrease in the efficiency of the degradation process of 95% to 60% (in the presence of H 2 O 2 ) aer four photocatalytic studies was observed.In this study, the photocatalytic experiments were extended to 2,4-DCP.In both studies, 57,58 the authors reported carboxylic acids and CO 2 as the degradation products of 4-CP.
Two studies were developed by Gül and co-workers 35,99 where they studied the degradation of 4-CP aer the incorporation of Co(II) and Zn(II) Pcs Co/Zn11 and Co/Zn15 (Fig. 4) into TiO 2 semiconductors.The results showed that under visible light (l > 400 nm), it was possible to achieve complete degradation of 4-CP in aqueous media aer 30 min with Zn11, Co11, Zn15, and Co15 (Table 3).Moreover, they observed that the MPcs were anchored into the surface of TiO 2 through CO-O-TiO 2 bonds.In the rst study, 99 recyclability studies showed a loss of 16% in the degradation of the pollutant using Zn11 and Co11 aer 5 cycles (Table 4).In the second study, 35 aer 5 cycles of the experiment, the majority of the photodegradation rate of 4-CP could be maintained (∼9% decrease) using Co15.On the other hand, there was a decrease of ∼16% in the degradation of 4-CP with Zn15.Herein, the authors extended the photocatalytic assays to chlorobenzene (PhCl) and 1,2,4-trichlorobenzene (TCB).None of these studies revealed the stability of the compounds under irradiation nor the degradation products of 4-CP.
3.1.5.Dichlorophenols.The contamination of wastewater with dichlorophenols is considered a severe threat.The toxicity of chlorophenol depends on the degree of chlorination and the substitution away from the ortho-position.There is reported increasing toxicity related to higher chlorinated phenolic compounds.The treatment of chlorophenols in wastewater is crucial to decrease their toxicity in water. 124Regarding the degradation of 2,4-DCP, Xu and co-workers 50 could achieve a complete degradation aer 60 min of visible light irradiation (l > 450 nm) by using Al4Cl-bentonite (modied with the surfactant cetyltrimethylammonium bromide) (Fig. 4) in aqueous media (pH = 12, Table 5).The photocatalyst's (photo) stability was neither reported nor recyclable studies.Moreover, the nal products of the degradation process were not identied.
Nyokong and co-workers, 54 on the other hand, could achieve ∼40% degradation of 2,4-DCP in aqueous media aer 30 min of visible light irradiation (l > 400 nm) by using Al3 immobilized on Amberlite ® (Fig. 4 and Table 5).2-Chloro-1,4-benzoquinone and formic acid were identied as the degradation products of 2,4-DCP.No stability or recyclability studies were reported for the catalyst.
The photodecomposition of 2,4-DCP in aqueous media was also assessed using sulfonated cobalt(II) phthalocyanine Co3 (Fig. 4) immobilized onto MCM-41. 59The immobilization of Co3 onto MCM-41 was performed through the ionic interactions between the cationic groups of the 3-(aminopropyl)triethoxysilane and the sulfonato groups of the phthalocyanine.The authors stated that both light and catalyst are essential for the degradation of 2,4-DCP since it could only be observed in the presence of the catalyst and light (visible or UV-A).When irradiated with UV-A light for 180 min, Co3 (0.6 g L −1 ) exhibited a higher decrease of 2,4-DCP degradation (93%) than when irradiated with visible light (55%) in the presence of H 2 O 2 .As indicated in Table 5, the presence of H 2 O 2 is essential when using the UV-A lightthe sample containing H 2 O 2 + Co3 could achieve 93% degradation aer 180 min of irradiation, while only 45% degradation was observed in the sample containing only Co3.Aer 4 cycles under UV-A irradiation, the photocatalytic degradation of 2,4-DCP could maintain up to 70%.The authors identied methyl pyruvate, dimethyl oxalate, dimethyl malonate, methyl levulinate, and methyl benzoate as the primary intermediates of 2,4-DCP degradation.However, the nal degradation products were simple acids like oxalic acid and acetic acid.
Xu and co-workers 47 and Pirbazari and co-workers 58 accessed the degradation of 2,4-DCPusing Al3 and Co3, respectively, adsorbed on TiO 2 as photocatalysts.The rst authors, 47 could achieve a complete degradation in aqueous media aer 420 min of visible light irradiation (l > 400 nm) with 1.0 wt% of Al3 loaded on TiO 2 (Table 5).There were no studies regarding the stability of the catalyst and the degradation products of 2,4-DCP.In the second study, they achieved 50% degradation of 2,4-DCP aer 180 min of visible light irradiation (l > 400 nm), which could be increased to 100% in the presence of H 2 O 2 .Moreover, aer four cycles, there was a loss of 40% in the photocatalytic oxidation of 2,4-DCP using Co3-TiO 2 .Regarding the degradation products of 2,4-DCP, the authors identied carboxylic acids and CO 2 .
Recently, Frajood and co-workers 60 could degrade 80% of 2,4-DCP within 135 min of visible light irradiation (l > 400 nm) by using Co4/nitrogen-doped graphene (N-GR).According to the authors, aer 3 cycles, there was a loss of 25% of activity.The authors identied carboxylic acids and CO 2 as the degradation products of 2,4-DCP.Zada, Dong, Fu, and co-workers 61 prepare a Zn4/g-C 3 N 4 nanocomposite for the photodegradation of 2,4-DCP.The authors could achieve a degradation of 85% aer 60 min of visible light irradiation (l > 420 nm).The enhanced catalytic activity of this nanocomposite is due to its high visible light absorption and effective generation of super oxide anions and holes.However, no studies were performed regarding the recyclability of the catalysts or degradation products of 2,4-DCP.
3.1.6.Trichlorophenols.Phenolic compounds such as trichlorophenols are widely used in the pharmaceutical, oil, paint, explosive, paper, and agrochemical industries.They are dened as priority pollutants.Their inappropriate disposal can damage the environment due to their potential toxicity to microorganisms, plants, and animals.These organic compounds are persistent and difficult to biodegrade. 125 and co-workers 47,50 reported two works regarding the degradation 58 of 2,4,6-TCP.In the rst study, 50 a complete degradation was achieved in less than 60 min using visible light irradiation (l > 450 nm) and Al4Cl-bentonite (modied with cetyltrimethylammonium bromide) in aqueous media (pH = 12).However, a gradual loss of activity was observed aer each catalytic cycle, and it might be due to the degradation of the surfactant by the generated singlet oxygen or by reducing the sorption process.In the second work, 47 the authors could achieve a 90% degradation in aqueous media aer 420 min of visible light irradiation (l > 400 nm) with 1.0 wt% of Al3 loaded on TiO 2 .No photostability studies of the catalysts nor the 2,4,6-TCP degradation products were reported.Nyokong and coworkers, 54 on the other hand, could achieve 30% degradation in aqueous media aer 30 min of visible light irradiation (l > 400 nm) by using Al3 immobilized on Amberlite ® (Fig. 4).The 2,5dichloro-1,4-benzoquinone was identied as the main degradation product of 2,4,6-TCP.Zanjanchi and co-workers 126 assessed the photodegradation of 2,4,6-TCP in aqueous media using visible light irradiation (l > 400 nm) and BiVO 4 -Silica composites graed with sulfonated cobalt phthalocyanine Co3 (Fig. 9).Different catalytic activities were observed depending on the silica and loaded phthalocyanine amount.The best results (∼100% degradation aer 240 min of irradiation) were obtained using the sample containing 15% silica graed with Co3; materials without the Co3 could only degrade 50% of 2,4,6-TCP.Regarding the stability of the composite, there was a leak of 15.2%, and the composite could be recovered and reused up to 4 times without signicant activity loss (3%).The degradation products were not identied, but the pH decrease during the assays could indicate the formation of carboxylic acids.
3.1.7.Pentachlorophenol.Chlorinated phenols, particularly PCP, are extremely toxic environmental pollutants.Their degradation in water is complex and may lead to chlorinated dibenzo-1,4-dioxins and other organic compounds that may be more toxic than the parent compound. 127yokong and co-workers 54,110 developed various materials for the degradation of PCP.In their rst work, 54 Al3, Zn3 (Fig. 4 and Table 6), Al18, Zn18 (Fig. 6 and Table 6), and a mixture of mono-, di-, tri-, and tetra-substituted sulfonated metalled phthalocyanines MPcS mix (M = Al(III), Zn(II), Ge(IV), Si(IV), or Sn(IV)) were immobilized on Amberlite ® .These materials were used as photocatalysts in the degradation of PCP in aqueous media (pH = 10) under visible light irradiation (l > 400 nm).The composites showed the following activity order aer 5 min of irradiation: Zn18 > SiPcS mix > SnPcS mix > ZnPcS mix > GePcS mix > Zn3 > AlPcS mix z Al18 > Al3.The Zn18/Amberlite was selected to perform the recyclability studies, where it was observed that there was only a 10% loss of activity aer three cycles.However, when performing homogenous photocatalysis, there was a 51% degradation of the catalyst (Zn2) aer 3 min of irradiation, which means that this phthalocyanine could not be applied to other pollutants as PCP since it needed more irradiation time.The tetrachloro-1,4-benzoquinone was identied as the major degradation product of PCP.Later, 110 they degraded PCP in a homogenous catalytic process in dichloromethane (DCM) with Pd26 (Fig. 6) and in a heterogeneous photocatalytic process in water with Pd26/ SWCNTs, both under visible light irradiation (l > 400 nm).It was possible to achieve a degradation rate of 70% and 30% in the homogenous and heterogenous processes, respectively.Again, tetrachloro-1,4-benzoquinone was identied as the major degradation product of PCP.The catalyst cannot be reused without a signicant loss of activity.Regarding the recyclability studies using 4-CP, the activity loss aer each cycle was less drastic than PCP.This can be due to the permanent adsorption of intermediates or products on the surface of the catalyst, thereby reducing the adsorption activity of the composite.Despite the low photocatalytic rates of Pd26/ SWCNTs hybrid, Pd26 had excellent photocatalytic activity by itself and, thus, may be applied in homogenous photocatalysis.
3.1.8.Other phenolic compounds.Other phenolic compounds like catechol, hydroquinone, salicylic acid, naphthol yellow S, and BPA are considered toxic to humans.][130][131] Xu and co-workers 47 reported the degradation of hydroquinone, catechol, salicylic acid, and 4-sulfosalicylic acid in aqueous media using 1.0 wt% of Al2 (Fig. 4) loaded on TiO 2 and visible light irradiation (l > 400 nm).Here, hydroquinone and catechol were degraded at 90% and 50%, respectively, aer irradiation for 420 min.However, only 20% and 10% degradation of salicylic acid and 4-sulfosalicylic acid were observed under similar conditions.Raducan and co-workers 86 reported  Review RSC Advances the photodegradation of naphthol yellow S using Cu3 (Fig. 4), Cu4 (Fig. 4), and Cu25 (Fig. 6) immobilized on TiO 2 .Notably, with Cu4, a maximum degradation of 18% was achieved aer 30 min under visible light irradiation (l > 400 nm).Jiang and coworkers 132 studied the photocatalytic degradation of BPA in aqueous media using polynuclear phthalocyanines M1 (Fig. 3) under visible light irradiation (l > 400 nm) for 40 min.Among the four complexes (Fe1, Cu1, Zn1, and Al1), the highest photocatalytic activity was obtained for Zn1.For this reason, only this photocatalyst was used to study the optimized conditions to degrade BPA.It is essential to highlight that Zn1 evidenced their decomposition during the photocatalytic process, and it is still possible to achieve a total degradation of the pollutant aer 20 min using a tungsten lamp.With solar irradiation, the same result was achieved aer 40 min.Regarding the degradation products, the authors could identify oxalic acid, hydroquinone, and 4-isopropenyl phenol.Wu, Xing, and co-workers 46 also studied the photodegradation of BPA but using Pd3 (Fig. 4) immobilized on FDU-15 mesopolymer.Herein, the photodegradation efficiency of BPA was also observed in aqueous media at different pH values, in the presence of H 2 O 2 , and under visible light irradiation.The pollutant was degraded within 60 min and 180 min when using 0.04 and 1.0 mmol L −1 , respectively.The degradation products were identied as dimethyl malonate, dimethyl oxalate, dimethyl D-malate, and CO 2 .The stability and photostability of the catalyst were not evaluated.In another study, Nyokong and co-workers 98 studied the photooxidation of BPA under visible light irradiation using indium(III) using the phthalocyanines In9 (Fig. 4), 30, 31Cl/PS bres (Fig. 8).The In31Cl/PS (t 1/2 = 178.0min) bre was the best photocatalyst followed by In9Cl/PS (t 1/2 = 267.0min) and In30Cl/PS (t 1/2 = 385.0min).
The photodegradation of BPA under UV light irradiation (l = 365 nm) in the presence of a ZnWO 4 /Mn17Cl material with 1 wt% Mn17Cl (Fig. 4) was investigated by Anucha and coworkers. 102It is highlighted that 60% of BPA was degraded aer 4 h of light exposure, but the degradation could be increased to 80% by adding H 2 O 2 .However, a complete degradation of BPA could be achieved aer 30 min only under visible light irradiation (l > 450 nm) and adding H 2 O 2 .

Organic dyes
Organic dyes are another group of water pollutants of signicant concern because many of the dyes used in industry are toxic to aquatic organisms.The wastewater from the dye industry has received attention in recent studies due to the toxicity of some raw materials (aromatic amines) used to produce the dyes.It has been shown that their disposal into the environment has led to severe contamination of signicant areas in some countries.Decolourizing these dyes is challenging due to their stability and complex structures.Current technologies used to eliminate these compounds are considered ineffective. 9,13n this review, the organic dyes were divided into six groups (Fig. 10): azo, triarylmethane, rhodamine, thiazine, xanthene, and anthraquinone dyes.
3.2.1.Azo dyes.Azo dyes represent 50% of the world's annual production, making them the largest synthetic dyes group.The name derives from their azo (-N]N-) functional group that can be found with other groups as aromatic rings.Due to their high production, their toxicity has been studied extensively.Their manufacturing was related to several cancer appearances and later proved that some azo dyes were carcinogenic. 133For this reason, the appearance of these dyes in wastewater could be considered a considerable health problem.In this review, we reported the studies of the degradation of nine azo dyes (Fig. 10): methyl orange (MO), methyl red (MR), acid orange 7 (AO7), orange G (OG), ponceau 4R (P4R), select brown (SB), sella fast black (SFB), basic red 29 (BR29), and reactive red 195 (RR195).
3.2.1.1.Methyl orange.MO is an unmanageable dye present in Nature that is hard to degrade and, if released into the environment, could cause severe threats to human health. 134he photocatalytic degradation of MO was studied by Nyokong and co-workers 100 in the presence of Zn9 (Fig. 4) immobilized into PSU bres to avoid aggregation.According to the authors, upon visible light irradiation, the use of PSU bre (t 1/2 = 135.9min) seems to reduce the ability of the degradation of MO when compared with the Zn9 (t 1/2 = 81.6 min) by itself (Table 7).Despite having higher half-life times and a lower degradation rate constant, degrading MO with the Zn9/PSU bres was possible.It is essential to highlight that with an increase in the MO concentration, the higher half-life time for Zn9.The same authors 84 also used a series of peripherally substituted zinc(II) and Lu(III)OAc phthalocyanine complexes 6-12 (Fig. 4) and 29 (Fig. 7) immobilized on PAA and PUR.In aqueous media, it was possible to degrade MO with the photoactive materials Lu7OAc/PS, Lu8OAc/PS, Lu12OAc/PS, and Lu29OAc/PS (Table 7) aer 150 min under visible light irradiation (l > 400 nm).These hybrids can degrade the MO slower (t 1/2 = 113.63-182.43 min) than 4-NP and 4-CP.The degradation of MO could be achieved faster with peripherally substituted Zn7/ PS bres (t 1/2 = 113.63min) when compared with their nonperipheral analogue (Lu29/PS) (t 1/2 = 130.78 min).
By conjugating silver nanoparticles and bres, the same authors 135 degrade MO using aand b-substituted zinc(II) phthalocyanines bearing carbazole groups 34 and 35 (Fig. 11), respectively.They linked them to silver nanoparticles, which were further immobilized in PS bres to be used in the photocatalysis of MO (Table 7).Under visible light irradiation (l > 400 nm), lower half-life times for the degradation of MO were achieved using the a-substituted Zn34/PS relative to the bsubstituted Zn35/PS.The photooxidation process increased in the presence of silver nanoparticles when compared with the phthalocyanines.
The photooxidation of MO and OG in aqueous media under visible light irradiation (l > 400 nm) with an aminefunctionalized cobalt ferrite (CoFe) magnetite magnetic nanoparticle (MNP) conjugated with zinc(II) phthalocyanines Zn40 and Zn42 (Fig. 12) was studied by Nyokong and co-workers. 142hese MNPs were embedded into electrospun polyamide-6 (PA-6) bres for support and catalyst regeneration aer the photocatalytic process.The authors compared the photocatalytic activity of CoFe-Zn40/PA-6 and CoFe-Zn42/PA-6 with CoFe/PA-6, Zn40/PA-6, and Zn42/PA-6 (Table 7) for the MO degradation experiment.Aer 60 min of irradiation, it was possible to achieve better MO degradation rates with the CoFe-Zn40 and CoFe-Zn42 compared with the respective electrospun Pcs and MNPs.
More recently, the same authors 143 studied the photodegradation of MO under visible light irradiation (l > 400 nm) with fabricated a-Fe 2 O 3 nanobres modied with the tetrasubstituted phthalocyanine Zn40 (Fig. 12) or monosubstituted phthalocyanine Zn41 (Fig. 12).It was possible to achieve a 50% degradation more rapidly using Zn41-a-Fe 2 O 3 (t 1/ 2 = 42.78min), followed by Zn40-a-Fe 2 O 3 (t 1/2 = 46.20 min) and a-Fe 2 O 3 (t 1/2 = 53.31min) (Table 7).The results show that sensitising a-Fe 2 O 3 with phthalocyanines reduced the half-life time, increasing the photocatalyst efficiency.By increasing the amount of MO, the half-life time was also increased.Aer reuse, there was a slight loss of activity as observed by an increase in the half-life times: Zn41-a-Fe 2 O 3 (t 1/2 = 45.00 min) > Zn40-a-Fe 2 O 3 (t 1/2 = 48.46min) > a-Fe 2 O 3 (t 1/2 = 69.30min).These authors reported in some of their studies 2-amino-5-(3-hydroxy-4-oxo-cyclohexa-2,5-dienylideneamino)benzene sulfonic acid and poly(catechol) as degradation products of MO. 84,100 Chen, Zhang, and co-workers 87 and Wang and co-workers 88 studied the degradation of MO in aqueous media under visible light irradiation with H 2 2/TiO 2 amorphous hybrid (Fig. 4) and nanocrystalline anatase TiO 2 with copper phthalocyanine Cu3 (Fig. 4), respectively (Table 7).In the rst study, 87 it was possible to achieve ∼80% of degradation with H 2 2/TiO 2 aer 180 min of light irradiation.These results are much higher when compared with H 2 4/P25 (50% within 180 min).At the same time, there was no degradation using pristine TiO 2 and H 2 2/SiO 2 .In the second study, 88 80% of MO could be degraded with the hybrid Cu3/TiO 2 within 60 min.The samples were heated at different temperatures, and the photocatalytic activity was again evaluated.Aer increasing the temperature, the dimeric form of Cu3 was disaggregated and vaporized or desorbed, and the amount of immobilized monomer was much higher when compared with the dimer.The excited state of the monomer has a much higher half-life than the aggregates, favouring the electron injection process.Gharagozlou and co-workers 89 evaluated the photooxidation of MO aer doping TiO 2 with Fe and preparing H 2 4 (Fig. 4)-Fe-doped TiO 2 (H 2 4/Fe-TiO 2 ) with different Fe doping content (0, 0.05, 0.5, and 3.0 mol% Fe).As expected, the Fe amount curiously inuences the activity of the TiO 2 composites.Under visible light irradiation (l > 400 nm) and in the presence of H 2 4/Fe-TiO 2 with different doping amounts of Fe, it was possible to observe the photocatalytic activity on MO (Table 7).The results showed that the degradation of MO is more effective using H 2 4/Fe-TiO 2 (t 1/2 = 19.8min) than using undoped H 2 4/ TiO 2 (t 1/2 = 23.1 min) and bare TiO 2 (t 1/2 = 138.6 min).These results can be due to electron-hole pairs' formation and electrons' transference from H 2 4 to TiO 2 .Also, according to the eld theory, Fe 2+ is unstable compared to Fe 3+ , and a release of a trapped electron occurs, returning to the Fe 3+ form.Initially, the photocatalytic degradation of MO increased with the increase of the doping amount of Fe on the composite, reaching a maximum activity of 0.5% and then decreasing with higher amounts of Fe.This activity can be explained by the fact that above 0.5 mol% of Fe, the Fe 3+ ions act as recombination centres for photo-generated electrons and holes, decreasing photocatalytic activity.
Regarding zinc oxide, Ahmed, Pal, and co-workers 90 developed a study of the degradation of MO using a hybrid containing zinc oxide nanorods and Zn4 (Fig. 4) (Zn4-ZnO) functionalized with two carboxyl groups of a tartrate molecule by interaction with the metallic zinc.According to Table 7, the authors performed the photocatalytic studies under red light (l = 620 nm) and white light irradiation (l > 365 nm).It was possible to degrade MO more efficiently with the hybrid material (35%) compared to bare ZnO (1%) aer 180 min of red light irradiation.The best results were obtained under white light irradiation (l > 365 nm), where the nanohybrid material Zn4-ZnO could achieve about 60% photocatalytic efficiency.
Xu, Li, and co-workers 136 studied the degradation of MO in an aqueous solution under visible light irradiation (l > 400 nm) by using substituted zinc(II) aminophthalocyanine Zn36 (Fig. 11) supported by functionalized multi-walled carbon nanotubes (MWCNTs).The authors proved by Raman spectroscopy that the covalent attachment of Zn36 to MWCNTs and the p-p interactions between these two entities induce the disaggregation of the Zn36.Aer 4 h, 86% of MO was degraded (Table 7).The authors also assessed these photocatalysts' ability to degrade Rhodamine B (RhB).
Liu, Zhao, and co-workers 91 studied the degradation of MO with Co4 (Fig. 4) immobilized onto MCM-41 under visible light irradiation.The authors established that either less or an excess amount of photocatalyst in the reaction solution impacted the degradation of MO.So, a low photocatalyst amount was insuf-cient to interact with all the MO molecules.However, an excess photocatalyst amount of Co3 caused a shielding effect in light penetration.It was possible to achieve 98% MO degradation aer 120 min of light irradiation with an optimal catalyst amount of 0.2 mg mL −1 (Table 7).Aer 4 cycles, it was possible to maintain a degradation rate of 90%.
Dabiri and co-workers 144 developed a study where they could degrade MO with nitrogen-doped carbon photocatalyst based a Performed at 11.0 mW cm −2 .b Amorphous TiO 2 .c P25 TiO 2 ; with.d 0.125.e 0.25, and.f 0.5 of (m Pc /m ZIF ) ratio.
Also, aer seven cycles, there was a loss of 4% in the degradation rate of MO.These studies were extended to RhB.More recently, Zang, Sun, Zhang, and co-workers 93 studied the degradation of MO in an aqueous solution under visible light irradiation (l > 420 nm) by using the Cu4 (Fig. 4) supported by poly(acrylamide-acrylic acid copolymer) hydrogel inverse opal beads (PACA HIOB).The authors assembled silica microspheres as sacricial templates and infused monomers within the pores for UV polymerisation to form the PACA HIOBs.Aer 20 min of light irradiation, there was a complete degradation of MO with a degradation rate of 0.0850 min −1 (Table 7).The authors also assessed these photocatalysts' ability to degrade other anionic dyes as Reactive red X-3B (RR3B), reactive black 5 (RB5), Remazol brilliant blue R (RBBR) and cationic dyes as RhB and Malachite green (MG).According to the authors, the degradation kinetics of the anionic dyes, except for RBBR, were faster than those of cationic dyes.The work of Zang, Sun, Zhang, and co-workers 93 was better than other hydrogel-based photocatalysts because the hydrogel-base inverse opal scaffold can increase light absorption, catalytically active sites, reduce charge transfer resistance and inhibit the recombination of photogenerated electron-hole pairs.Regarding MO, the authors did not study the degradation products or the recyclability of the photocatalyst.
3.2.1.2.Methyl red.MR is an azo dye that appears in textiles and other commercial products.This dye can cause eye and  skin sensitization and digestive tract irritation when swallowed, and thus, it is important to remove it from wastewater. 145yokong and co-workers 103 studied the degradation of MR in aqueous media (pH = 7.4) with a covalently linked In18Cl to MNP already functionalized with (3-aminopropyl)triethoxysilane (Fig. 13).The use of MNP allows the catalyst to be recovered several times with magnetic separation.Furthermore, In18Cl and its conjugate with MNP have been embedded in PAN electrospun bres.Under visible light irradiation (l > 400 nm), it was possible to degrade more efficiently the MR with the MNP-In18Cl/PAN, given the lower time of half-life (t 1/2 = 29.5 min) and higher degradation rate (k obs = 0.0235 min −1 ).Aer the reuse of the catalyst, there was a slight decrease in the MR degradation rate and an increase in the half-life time.In this study, the authors did not perform stability studies, but they mentioned that the conjugates are stable because, during the singlet oxygen generation assays, the Q bands of the compounds remained intact on their absorption spectra.
3.2.1.3.Acid orange 7 (or orange II).Acid orange 7 (AO7), also known as orange II, is an azo dye extensively used for dyeing wool.This dye is non-biodegradable, and for that reason, its removal from wastewater is needed. 146Nowakowska and coworkers 147 studied its degradation in aqueous media under visible light irradiation (l = 400-550 nm) using the uorinated phthalocyanine Zn43 (Fig. 14) immobilized into bentonite as the photocatalyst.A degradation of 80% was observed aer 200 min of light irradiation.Reusability studies showed that the catalyst could be reused four times without signicant activity loss (15%).
The degradation of AO7 in aqueous media using visible light irradiation was also evaluated by Schneider and co-workers 104 in the presence of Cu18 (Fig. 6) immobilized on g-C 3 N 4 .A maximum degradation rate of 95% was achieved aer 180 min of light irradiation with 0.5 wt% of Cu18.Recyclability studies of the catalyst revealed a slight decrease in activity (5% loss) aer ve cycles.Qu and co-worker 141 selected AO7 as a target pollutant for their decomposition, evaluating the use of cobalt(II) phthalocyanine Co37 (Fig. 11) immobilized on activated carbon bres.The AO7 removal was enhanced using Co37/carbon bres as a catalyst and UV light irradiation (l = 365 nm).In fact, within 120 min of irradiation, there was a 23% enhancement in the dye removal.The best photocatalytic rate (47%) was achieved using a 2 g L −1 catalyst concentration.The authors also assessed the inuence of H 2 O 2 addition, where it was possible to achieve 99% of the photodegradation rate within 60 min of irradiation with a concentration of H 2 O 2 of 12.5 mmol L −1 .Aer four cycles, the photocatalytic rate was still above 92%, meaning no signicant activity loss occurred.
3.2.1.6.Reactive black 5. RB5 is most widely used for dying cotton and other cellulose bres.There is a huge consumption of this dye in industry. 149Zang, Sun, Zhang, and co-workers studied 93 the degradation of RB5 in an aqueous solution under visible light irradiation (l > 420 nm) by using the Cu4 (Fig. 4) supported by PACA HIOB.Aer 20 min of light irradiation, there was a complete degradation of RB5 with a degradation rate of 0.0772/min.The authors also assessed these photocatalysts' ability to degrade other anionic dyes such as Reactive red X-3B (RR3B), RBBR and cationic dyes such as RhB and Malachite green (MG).Regarding RB5, the authors did not study the products of degradation or recyclability.
3.2.1.7.Basic red 29 and reactive red 195.Azo dyes like BR29 and RR195 are resistant to biodegradation under aerobic conditions, whereas anaerobic treatment could be applied successfully.However, anaerobic processes cannot be used in wastewater treatments because the breakdown of these dyes can form aromatic amines, which are considered more toxic than the dyes themselves. 150,151he degradation of BR29 and RR195 using Fe4/AT-PAN and Fe4/PAN (Fig. 6) was studied in aqueous media under visible light irradiation by Han, Zhao, and co-workers. 63In the presence of H 2 O 2 , it was possible to have a complete degradation of RR195 with and without light irradiation with the AT-PAN as a catalyst.On the other hand, only 20% of RR195 could be degraded either in the presence or absence of light, showing no difference in using an irradiation system for both dyes.Regarding the PAN bres catalyst, the inuence of visible light is noticeable, with an increase in the degradation rate of 50-90% for BR29 and 40-80% for RR195, respectively.The degradation products of these dyes were not identied, and the authors did not perform stability and photodecomposition studies of the catalysts.
3.2.1.8.Reactive red X-3B.RR3B is an azo dye used in fabric dyeing and represents almost 60% of the total dyes used in the dyeing industry.Due to their toxicity, its discharge into the water will threaten aquatic and human organisms. 152Zang, Sun, Zhang, and co-workers 93 studied the degradation of RR3B in an aqueous solution under visible light irradiation (l > 420 nm) by using the Cu4 (Fig. 4) supported by PACA HIOBs.Aer 15 min of light irradiation, there was a complete degradation of RR3B with a degradation rate of 0.1218 min −1 .Aer ve cycles, the degradation efficiency was still 98.1%.The authors also assessed these photocatalysts' ability to degrade other anionic dyes, such as RBBR and cationic dyes, such as RhB and Malachite green (MG).Regarding RR3B, the authors did not study the degradation products.
3.2.2.Triarylmethane dyes.Triarylmethanes are one of the most used types of dyes in the textile industry.These dyes are considered toxic and carcinogenic.There are some physicochemical methods that are already used to degrade these dyes, but they are considered inefficient and expensive and can produce by-products that can be more toxic than the dyes. 153In this section, crystal violet (CV), bromophenol blue (BPB), brilliant blue (BB), and fuchsine (FS) are used as model pollutants.
3.2.2.1.Crystal violet.CV is considered carcinogenic with acute cytotoxicity to some animals and plants.The inadequate discharge into the environment can cause some serious health problems. 154For the degradation of CV, Mohamed and coworkers 155 used a composite based on ZnO and Cu44 (Fig. 15) and a solar simulator as an irradiation source.A complete degradation was achieved with the composite Cu44/ZnO in the presence of H 2 O 2 (80% in the absence of H 2 O 2 ) aer 40 min of irradiation in aqueous conditions (pH = 5).These results showed an enhancement of the photocatalytic activity compared with bare ZnO and Cu44.There was a decrease of 10% in the photocatalytic degradation of CV aer three cycles of the experiment.
3.2.2.2.Bromophenol blue.BPB is a triarylmethane dye considered hazardous for all living beings, negatively affecting photosynthesis in aquatic organisms.It is considered carcinogenic, mutagenic, and allergenic. 156For the BPB degradation in  14).BB was a popular colorant in the textile industry and used as a common food additive.Due to its toxic effects on humans and animals, it was banned.It is reported to be carcinogenic, causing reproductive and neurological disorders, allergies, and trouble breathing. 158FS is also carcinogenic and mutagenic and has a very slow degradation in Nature. 159aducan and co-workers 86 studied the degradation of BB and FS in aqueous media using Cu3-TiO 2 (Fig. 4), Cu4-TiO 2 (Fig. 4), and Cu25-TiO 2 (Table 9).Regarding the recyclability studies, the authors selected Cu3-TiO 2 as the catalyst and BB as the pollutant.The results showed that aer 10 cycles a photodegradation rate of 20% was achieved for the selected dye.
3.2.2.4.Malachite green.MG is an extensively used biocide in aquaculture with genotoxic and carcinogenic properties. 160o, Zang, Sun, Zhang and co-workers 93 studied the degradation of MG in an aqueous solution under visible light irradiation (l > 420 nm) by using the Cu4 (Fig. 4) supported by PACA HIOBs.MG was degraded entirely aer 40 min of light irradiation with a degradation rate of 0.0601 min −1 .The authors also assessed these photocatalysts' ability to degrade other anionic dyes, such as RBBR and cationic dyes, such as RhB.Regarding MG, the authors did not study the degradation products or the recyclability of the photocatalyst.
3.2.3.Rhodamine dyes.Rhodamines are used for dye laser materials, but they are considered the most toxic dyes in the textile industry because of their high stability and non-biodegradable properties.This review will discuss the photodegradation of Rhodamine B (RhB) and Rhodamine G (RhG).Both dyes are classied as carcinogenic and neurotoxic, causing respiratory tract infections.When inhaled and ingested, they can cause liver and thyroid damage and eye and skin irritations.The traditional methods to remove these dyes require a complex treatment and present several disadvantages, such as high energy consumption and the formation of toxic by-products. 161,162.2.3.1.Rhodamine B. RhB is a dye used in the textile industry and in food processing.However, since it has been classied as carcinogenic, it has been forbidden from being used in food processing for decades.Several strategies exist to obtain MPcs with high oating properties, like making phthalocyanine super-hydrophobic.So, for the degradation of RhB in aqueous media under visible light irradiation (l > 400 nm), Shao, Chen, and co-workers 64 used a hierarchical nanostructure with a hollow interior space composed of zinc(II) phthalocyanine Zn4 (Fig. 4).Within 660 min, 89% of the RhB was photodegraded in the presence of the hierarchical tubular structure (Table 10).
Conjugated microporous polymers (CMP) are crosslinked polymers that merge porosity and extended p-conjugated systems.Their building blocks are spatially segregated to suppress the p-p interaction.They have a high surface area, rigid backbone, and high thermal stability. 163So, Duan and coworkers 65 studied in aqueous media the degradation of RhB in the presence of H 2 O 2 with a series of metallophthalocyaninebased microporous polymers M45-CMP (M = Co(II), Cu(II), or Zn(II), Fig. 16) and visible light irradiation (l > 400 nm, Table 10).
The authors discovered that the efficiency of the photocatalytic activity on RhB was improved when the amount of catalyst increased, but an excessive amount of catalyst proved useless for the system.Also, when comparing the photocatalytic activity of Co45-CMP with the monomer Co5, the polymer Co45-CMP showed an enhanced photocatalytic activity (∼100% aer 30 min of irradiation vs. 80% aer 150 min of irradiation).Aer discovering the ideal conditions, the three photocatalysts' ability to degrade RhB was accessed under the same conditions (15 mg of M45, in H 2 O 2 ).It was possible to complete the degradation of RhB aer 30 min with Co45-CMP (∼100% of degradation aer 30 min of irradiation).On the other hand, it was only possible to degrade 50% of RhB with Cu45-CMP and Zn45-CMP aer 180 min of light irradiation.The best photocatalytic rate with Co45-CMP could be maintained without a signicant decrease aer four experiments.The authors mentioned that these results indicate that the MPc-CMPs can potentially apply to the environmental purication of organic pollutants in industrial wastewater.
Another study of the RhB degradation in an aqueous media was performed by Wang and co-workers 164 using a chitosansupported cobalt(II) phthalocyanine Co46 (Fig. 16) membrane under UV light irradiation.According to the authors, chitosan is linked to the phthalocyanine Co46 through a sulfonamide bond established between the chlorosulfonyl groups and the amino groups of the chitosan.There was a 99% degradation of RhB with the polymer aer 60 min (Table 10).Aer ve experiments, retaining 60% of the degradation rate was possible.Han, Zhao, and co-workers 63 studied the photooxidation for RhB in aqueous media using iron(II) phthalocyanine Fe4 (Fig. 4) immobilized onto copper(II)-amidoximated polyacrylonitrile bre (AT-PAN), visible light, and H 2 O 2 .The amidoxime groups aided in the anchoring process of Fe4 to the PAN bre through coordination interaction.The authors prepared two different catalysts: one containing unmodied PAN bres and the other containing the AT-PAN.When using either catalyst, complete degradation of RhB was achieved in the presence of H 2 O 2 within 60 min (Table 10).Aer 5 cycles, it was only observed a 12% decrease in the photodegradation rate.Regarding the degradation products, they reported the ones presented in Fig. 17.At the end of the photocatalytic assay, the authors could nd carboxylic acids and alcohol as the nal products of RhB.For the degradation of the same pollutant in aqueous media, Xin and co-workers 66 and Varghese and co-workers 34 used TiO 2 sensitized with Zn4 (Zn4-TiO 2 , Fig. 4), Fe4 or Co4 and visible (l > 400 nm) or simulated solar light.In the rst study, 66 the authors prepared TiO 2 nanoparticles through a hydrothermal method with posterior impregnation of the Zn4.According to the results, the Zn4-TiO 2 has an extended absorption band into the visible region compared to bare TiO 2 (Degussa P25).This photophysical feature induces a higher photocatalytic activity under the simulated solar light and visible light (l > 400 nm) when compared with bare TiO 2 .As expected, this difference is more pronounced under visible light than simulated solar light (Table 10).In the second study, 34 under solar irradiation and using Fe4/TiO 2 , Co4/TiO 2 , and bare TiO 2 , it was possible to degrade 88%, 73%, and 78%, respectively (Table 10).Despite promising photocatalytic activities, evaluating the stability of compounds within several cycles would be essential.
Still studying the degradation of RhB in aqueous media, Sosa-Sánchez and co-worker 165 used a hybrid photocatalyst with the non-symmetrical zinc(II) phthalocyanine Zn51 (Fig. 18) and visible light.This hybrid was compared to the individual molecules (TiO 2 and Zn51) to evaluate the sensitization effect on their photocatalytic efficiency.It was observed that an improvement in the photocatalytic degradation of RhB occurred aer sensitization of the TiO 2 .Aer 180 min, there was a decrease of 90% in the concentration of RhB (Table 10).Shao, Mu, and co-workers 67,68 accessed the photooxidation of RhB using photocatalysts based on hierarchical nanostructures with Cu5 (Fig. 4) immobilized on electrospun TiO 2 nanobers and the loading of Fe5 (Fig. 4) nanosheets on one-dimensional carbon nanobers.In the rst study, 67 the photocatalytic degradation of RhB under visible light irradiation (l > 400 nm) showed that the 1 : 50 (molar ration) Cu5/TiO 2 nanobers could achieve a degradation rate of 38% aer 4 h, much higher than bare TiO 2 nanobers (Table 10).Aer increasing the molar ratio to 1 : 20, 87% degradation was achieved within 240 min.In the second study, 68 Fe5 nanosheets were uniformly distributed on the surface of each bre without enhancing an aggregation phenomenon, offering a high surface area of the nanosheets.In the synthetic approach, the Fe5 nanosheets were grown onto the surface of the carbon bres, which was proved by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).In the photocatalytic studies, aer 180 min under visible light irradiation (l = 400 -700 nm), the Fe5/carbon bres could achieve a 91% degradation rate.It is important to highlight that pure Degussa P25 (TiO 2 used as a comparison), Fe5, and carbon bres did not exhibit high photocatalytic rates, reaching 27%, 35%, and 46% within the same irradiation time.The Fe5/carbon bres could be reused (aer separation by sedimentation process) for up to three cycles, maintaining the same photocatalytic activity.The authors also prepared two other materials by increasing the amount of the Pc starting materials to 2 times (2-Fe5/carbon bres) and 4 times (4-Fe5/ carbon bres) higher than the initial one to nd the ideal amount of Fe5 nanostructures.They observed that it was possible to degrade RhB more efficiently with 2-Fe5/carbon bres, followed by Fe5/carbon bres and 4-Fe5/carbon bres.
Still using visible light (l > 400 nm), Das, Chattopadhyay, and co-workers 69 studied the photooxidation of RhB in aqueous by using a copper(II) phthalocyanine Cu4 (Fig. 4) functionalized with reduced graphene oxide (rGO) nanocomposite.Compared with Cu4, the degradation efficiency using the rGO/Cu4 nanocomposite was higher due to the redshi in the absorption spectrum that increases the catalytic activity under visible light (Table 10).The degradation efficiency reached 96% aer 210 min of light irradiation when rGO was twice bigger than the Cu4 in the nanocomposite.The rGO played an essential role in enhancing the degradation efficiency due to the formed donoracceptor system.
Li, Xu, and co-workers 70,136,139 evaluated the degradation of RhB in aqueous media with visible light (l > 400 nm) and composites of zinc(II) phthalocyanine Zn4 (Fig. 4), Zn36, and Zn38 (Fig. 11) with MWCNTs.In the rst study, 136 there was almost no degradation rate (∼19%) using MWCNTs due to the high specic surface area of these CNTs.Aer immobilization with Zn36 and aer 240 min, it was possible to degrade 88% of RhB with the hybrid Zn36-MWCNT.More importantly, aer three cycles, the degradation efficiency for RhB did not suffer any signicant change (just a slight decrease of 4%).Regarding the second study, 70 of the pure Zn4, MWCNTs, and Zn4/ MWCNT hybrids exhibited a photodegradation efficiency of 54%, 4%, and 93%, respectively, within 60 min of irradiation (Table 10).The hybrid material reveals a superior photocatalytic activity compared with pure Zn4 and MWCNTs due to the MWCNTs that prevented the Zn4 aggregation and increased the catalytic active sites.According to the authors, the photocatalytic rate did not signicantly change (89%) aer reusing the Zn4/MWCNT for three consecutive experiments.In the later study, 139 aer 120 min of irradiation, it was possible to achieve 93% of RhB degradation with hybrid Zn38-MWCNTs when compared with bare MWCNT (14%) and Zn38 (54%).
Zhang and co-workers 166 photodegraded RhB in aqueous media using Cu47/perylene diimide (PDIC12) (Fig. 19) p-n heterojunction under visible light irradiation (l > 400 nm).This composite was based on the intramolecular hydrogen bond between the pyridyl moiety of the perylene and the carboxy group of Cu47.][171] and Cu47).Also, a higher molar fraction of the PDIC12 derivative on the composite allowed a higher photocatalytic degradation rate of RhB, reaching 80% aer 180 min (Table 10).
Still using PAN bres and RhB as a pollutant under visible light and solar irradiation, Lu, Chen, and co-workers 56 studied Fig. 17 Degradation products of RhB reported by Han, Zhao, and co-workers. 63ts degradation in aqueous media using a photocatalyst based on PAN-supported g-C 3 N 4 coupled with Zn(II) phthalocyanine 2 (Fig. 4) nanobers.In the visible light studies, the removal rate of RhB using g-C 3 N 4 /Zn2/PAN as photocatalyst was higher than g-C 3 N 4 /PAN, reaching a maximum of ∼98% aer 120 min of light irradiation (Table 10).Under solar irradiation, almost a complete degradation of RhB was achieved aer 180 min with the g-C 3 N 4 /Zn2/PAN.The degradation rate could be maintained aer three cycles of experiment with g-C 3 N 4 /Zn2/PAN.The rst degradation products are presented in Fig. 20.Aer this, these intermediates are degraded into the ones mentioned by Han, Zhao, and co-workers 63 (Fig. 17).
By also using solar irradiation, Oki and co-workers 74 studied the photooxidation of RhB using graphene-ZnO composite with a Co4 (Fig. 4).There was a complete degradation using GR-ZnO and GR-ZnO-Co4 aer 140 and 150 min under sunlight irradiation, respectively (Table 10).On the other hand, there was only a 20-60% degradation when using the Co4, ZnO, and GR alone as catalysts.Under the same experimental conditions, the degradation efficiency of GR-ZnO-Co4 was found to be higher than GR-ZnO catalyst.The interactions between the GR nanosheets and ZnO particles enhanced the photocatalytic activity of the GR-ZnO composite when compared with bare GR and ZnO.The GR nanosheets were the main ones responsible for the absorption of RhB and its posterior degradation.The sensitization with Co4 enhances the composite's absorption ability, increasing the photocatalytic efficiency.Still regarding the degradation of RhB and using the same phthalocyanine 8 but with N-PC (Cu4/N-PC), Dabiri and co-workers 144 prepared a series of hybrids with different weight ratios: Cu4 0.125 /N-PC, Cu4 0.25 /N-PC, and Cu4 0.5 /N-PC.Aer 90 min of visible light irradiation (l > 400 nm), there was no degradation for RhB with Cu4 0.125 /N-PC.However, it was possible to observe a more efficient photocatalytic degradation with Cu4 0.25 /N-PC (0.0627 min −1 ) than with Cu4 0.5 /N-PC (0.0551 min −1 ) in the presence of H 2 O 2 .Also, aer performing seven experiments with the best photocatalyst, it was possible to maintain most of the activity (4% loss) -Table 10.
Huang and co-workers 168 studied the photooxidation for RhB in aqueous media under visible light irradiation (l > 420 nm) with a tetra-substituted manganese(II) phthalocyanine bearing sulfonic acid groups Mn3 (Fig. 4) immobilized on a TiO 2 -SiO 2 hybrid support.Aer 240 min of irradiation, complete degradation of RhB was achieved (Table 10).Under visible light irradiation (l > 400 nm), Chen and co-workers 106 studied the degradation of RhB using a magnetically recyclable composite AT/Fe 3 O 4 -Fe18 (Fig. 6).This composite was prepared using Fe18 and magnetic palygorskite nanoparticles (AT/Fe 3 O 4 ).The remarkable superparamagnetic properties of this composite allow their recuperation by simply applying an external magnetic eld.Different composites were prepared based on the amounts of phthalocyanine.The photodegradation rate was 96% aer 300 min of light irradiation (Table 10) using Fe18 (0.6 nmol).However, the best photocatalytic activity was obtained with higher amounts of Fe2 (0.6 nmol).More recently, Zang, Sun, Zhang, and co-workers 93 studied the degradation of RhB in an aqueous solution under visible light irradiation (l > 420 nm) by using the Cu4 (Fig. 4) supported by PACA HIOBs.Aer 40 min of light irradiation, there was a complete degradation of RR3B with a degradation rate of 0.1218/min.Aer ve cycles, the degradation efficiency was still 97.3%.The authors also assessed these photocatalysts' ability to degrade other anionic dyes, such as RBBR.Regarding RhB, the authors did not study the degradation products.
3.2.3.2.Rhodamine 6G.As RhB, RhG is also a chemically stable dye that is difficult to degrade. 75Nyokong and coworkers 75 evaluated the photocatalytic degradation of RhG in aqueous media using bare zinc(II) tetraaminophthalocyanine Zn6 (Fig. 4) or conjugated with Ag nanoparticles.Both were incorporated into chitosan beads to facilitate the recovery aer photocatalysis.In the presence of Ag nanoparticles, the photocatalytic degradation under visible light irradiation (l > 400 nm) of RhG was enhanced (t 1/2 = 41 min) when compared with Zn6 immobilized onto chitosan beads (t 1/2 = 46 min, Table 10).Besides Ag nanoparticles, the previous authors 137 also used the peripherally substituted phthalocyanine 35 (Fig. 11) but conjugated with ZnO affording Zn35-ZnO/PS bres.The authors compared this composite's photocatalytic activity against RhB with Zn35-AgNPs/PS bres.ZnO and AgNPs signicantly improved the photocatalytic activity of the composites, being Zn35-AgNPs/Ps a better photocatalyst (shorter half-life times and higher degradation rate constant) compared to Zn35-ZnO/ PS bres (Table 10).The structure of the products was not identied, but the authors mentioned some peaks in the HPLC analysis that could be attributed to the removal of the diethyl group from the nitrogen atom, as presented in Fig. 20.3.2.4.Thiazine dyes.Thiazine dyes are a class of heterocycles with a low oxidation potential and a high propensity to  form stable cations.When inadequately discharged, they can cause harmful impacts due to their high toxicity. 172.2.4.1.Methylene blue.Methylene blue (MB) has been shown to cause central nervous system toxicity.When released into wastewaters without treatment, it can cause a serious threat. 173So, Vallejo and co-workers 174 studied the degradation of MB in aqueous media under visible light irradiation using Cu(II)2 and Zn(II)2 (Fig. 4) immobilized on TiO 2 .Aer 140 min, it was possible to achieve 47% and 30% of RhB degradation, respectively, which were 2.8 times and 3.6 times better than bare TiO 2 (7%) (Table 11).
Using TiO 2 and Pc 4, Kwak, Chung, and co-workers 76 and Varghese and co-workers 34 both studied the degradation of MB in aqueous media under visible light irradiation with TiO 2 /Zn4 hybrids with several pore sizes and or sensitized TiO 2 with M4 (M = Co(II) or Fe(II)) to form M4/TiO 2 composites.In the rst study, 76 as expected, no MB degradation was observed within 90 min in the presence of all hybrids and the absence of light.The hybrids incorporating Zn4 showed higher photocatalytic activity when compared with the unmodied samples.The photocatalytic degradation efficiencies against MB were 85%, 90%, 70%, 67%, and 42% for L121-TiO 2 /Zn4 (3.7 nm of pore size), P123-TiO 2 /Zn4 (3.9 nm of pore size), F68-TiO 2 /Zn4 (3.6 nm of pore size), F127-TiO 2 /Zn4 (3.8 nm of pore size), and Degussa P-25/Zn4, respectively (Table 11).Herein, it was shown that the size of the pores did not inuence the photocatalytic activity.The high photocatalytic activity is due to a cascade of Mie light scattering.The pore size of P123-TiO 2 /Zn4, which is comparable with the wavelength of the irradiation source, strongly generated the Mie scattering, followed by a considerable enhancement of the photocatalytic activity.In the second study, it was possible to achieve higher photocatalytic rates using Fe4/TiO 2 (97%) when compared with Co4/TiO 2 (91%) and bare TiO 2 (81%) aer 90 min under solar irradiation (Table 11).Despite having promising photocatalytic activities, it would be essential to evaluate the stability of the compounds within several cycles in future work.
For the degradation of MB in aqueous media, Zahmakiran, Agirtas, and co-workers 169 also studied their photooxidation using a copper(II) phthalocyanine Cu48 (Fig. 16) immobilized in TiO 2 .MB was degraded entirely within 90 min under visible light irradiation (Table 11).Aer ve cycles, the photocatalyst could retain > 80% of its initial activity.
The degradation of MB in aqueous media under visible light irradiation (l > 400 nm) was performed using free-base and metallophthalocyanine M52 (M = Zn(II), Co(II), Ni(II), or Cu(II), Fig. 21) immobilized on TiO 2 by Gorduk, Avciata, and coworkers. 38According to the authors, within 100 min, it was possible to achieve complete degradation of MB using all the composites.Aer being reused up to ve times, they could maintain their activity above 76%.
Schneider and co-workers 104 could degrade 98% of MB in aqueous media within 270 min under visible light irradiation using Cu18 (Fig. 6) immobilized in g-C 3 N 4 (Table 11).Under UV (l = 365 nm) or visible light (l = 400-700 nm) irradiation, Maya-Treviño and co-workers 77 studied the photodegradation for MB using Cu4 (Fig. 4) sensitized on ZnO through a sol-gel method.The authors prepared two materials varying the percentage containing Cu4.The rst material contains 0.1% wt, and the second comprises 0.5% wt.According to the authors, aer 120 min under visible light irradiation, it was possible to achieve 98% degradation for MB (Table 11).Compared with TiO 2 (a widely known photocatalyst), it could only achieve similar percentages aer 180 min of light irradiation.Under UV light irradiation, the same activity could be achieved aer 150 min under light exposure.Li, Liang, and co-workers 176 achieved a 90% degradation for MB in aqueous media aer 120 min under visible light irradiation (l > 420 nm) using a zirconiumbased MOF, UIO-66 (NH 2 ), covalently linked to Zn53 (Fig. 21).This photocatalytic rate was much higher when compared with a mixture of Zn53 and UIO-66(NH 2 ) (Table 11).Also, aer four cycles, the photocatalytic activity decreased to 20%.
Wang, Liu, and co-workers 170 studied the degradation of MB in aqueous media using Zn49 (Fig. 16) immobilized in three different polyoxometalates (POMs): P 2 W 17 , P 2 W 18 , and PW 12 .Under visible light irradiation (l > 400 nm), achieving complete degradation aer 240 min and 450 min was possible using Z49/ PW 12 and Zn49/P 2 W 17 , respectively.However, aer 450 min, only 20% of MB degradation was achieved using Zn49/P 2 W 18 .A degradation rate of 100% was achieved with Zn49/P 2 W 17 with a small photocatalyst dosage (Table 11).Still using visible light irradiation (l > 400 nm), Liang, Li, and co-workers 78,138 studied the photooxidation of MB in aqueous media with sulfur-doped g-C 3 N 4 (CNS) coupled with zinc(II) phthalocyanines Zn36 (Fig. 11), Zn4 (Fig. 4), and Zn52 (Fig. 21).In the rst study, 78 composites exhibited higher photocatalytic degradation (39-97%) than bare CNS (30%).Zn36/CNS degrade ∼97% of MB aer 100 min under irradiation.On the other hand, with Zn52/ CNS and Zn4/CNS, the photocatalytic rate decreased to 82% and 39%, respectively (Table 11).In the second study, 138 the pure g-C 3 N 4 and Zn36 showed degradation efficiencies of 36% and 42%, respectively, within 120 min of irradiation.Incorporating sulfur in the g-C 3 N 4 enhanced the photocatalytic activity of the catalysts.The activities of the composites followed the order: g-C 3 N 4 < Zn36 < g-CNS < Zn36/g-C 3 N 4 < Zn36/g-CNS.Aer three cycles, there is a decrease of 30% in the photocatalytic efficiency of the Zn36/g-CNS.Liu and co-workers 177 studied the degradation of MB in aqueous media under visible light (l > 400 nm) with cobalt(II) phthalocyanine Co3-sensitized hollow Fe 3 O 4 @-SiO 2 @TiO 2 hierarchical nanostructures (Fig. 22).According to the authors, the composite showed better photocatalytic activity, reaching ∼100% degradation of MB aer 30 min of irradiation compared with the UV-visible light (60 min).The photocatalyst could be separated by an external magnetic eld and reused for three cycles without signicant activity loss.
Karaoglan and co-workers 178 could completely degrade MB using M54 (M = Zn(II), Co(II), Cu(II), and TiO(IV)(OPr)) (Fig. 24) Fig. 21 Tetra-a-substituted phthalocyanines 52 38,78 and 53 176 developed by Gorduk and Avciata, 38 Li and Liang 78,176 and co-workers.and visible light irradiation (l > 420 nm) in aqueous media.Aer 110 min, it was possible to completely degrade MB using Zn54 and Co54, whereas it took Cu54 and Ti54O 130 min to achieve the same degradation.Aer 3 reusability cycles, there was only a loss of 18% for all the photocatalysts.The authors did not study the degradation products of MB.
3.2.5.Xanthene dye -uorescein.Xanthene dyes are characterized by their intense uorescence, being uorescein the most well-known example.This dye is the most common marker for maritime accidents or tracers for underground rivers.For this reason, it is commonly found in wastewater. 179inding an environmentally friendly process to degrade this pollutant is a very attractive task.So, for the photodegradation of uorescein (FC) in aqueous media under visible light, Raducan and co-workers 86 used Cu3-TiO 2 , Cu4-TiO 2 (Fig. 4), and Cu25-TiO 2 (Fig. 6).The different photocatalytic activities of these nanocomposites in aqueous media revealed that the best photocatalyst was Cu3-TiO 2 (90%), followed by Cu25-TiO 2 and Cu4-TiO 2 .However, when using bare TiO 2 , a 90% photodegradation rate was also achieved, meaning that no improvement was observed with the addition of the phthalocyanines.Regarding the recyclability studies, the authors selected Cu3-TiO 2 and performed it in another dye: brilliant blue.
3.2.6.Anthraquinone dyeremazol brilliant blue R. Anthraquinone dyes, more specically, RBBR is a vinyl sulfonebased formazan dye known for its bright color, easy application techniques, low energy consumption in the dyeing process and high-water solubility.Its discharge into the environment can seriously harm organisms in aquatic life due to their toxicity, carcinogenicity, and non-biodegradability. 180 So, Zang, Sun, Zhang and co-workers studied 93 the degradation of RBBR in an aqueous solution under visible light irradiation (l > 420 nm) by using the Cu4 (Fig. 4) supported by PACA HIOB.Aer 40 min of light irradiation, there was a complete degradation of RBBR with a degradation rate of 0.0461/min.Regarding RBBR, the authors did not study the degradation products or recyclability.

Agrochemicals
Agrochemical and pharmaceutical compounds play very important roles in modern society, providing greater quantity and quality of food as well as health and well-being for the entire population.However, due to the worldwide massive amounts of used agrochemicals (mainly insecticides, fungicides, and herbicides), their negative impact on the environment is unquestionable.When these compounds reach humans, they can cause neurotoxic, endocrine-disruptor, and DNA-damaging effects. 181The photodegradation of dichlorvos, 2,4-dichlorophenoxyacetic acid, and fenamiphos (Fig. 25), catalysed by phthalocyanines, is discussed in the following sections.
3.3.1.Dichlorvos.Dichlorvos (Fig. 25) is an organophosphate used as an insecticide to control household pests.It is soluble in water and difficult to degrade or absorb sediment.Its toxicity appears as an irreversible inhibitor of acetylcholinesterase.This inhibition causes an accumulation of acetylcholine in synapsis, providing a disruption of nerve function. 182So, its degradation becomes crucial when found in wastewater.For this reason, Núñez and co-workers 183 studied the photodegradation of dichlorvos in aqueous media (pH = 7) with Cu3 (Fig. 4) adsorbed on TiO 2 -Degussa P25 and UV and/or visible light irradiation.Under visible light, the best photocatalytic activity was obtained when using Cu3-TiO 2 (k obs = 0.7 × 10 2 min −1 ) with a lower surface coverage area (q = 9%).Under UV light, anatase TiO 2 could achieve a high rate of dichlorvos degradation: k obs = 1.0 × 10 2 min −1 .Under simulated solar light (visible + UV), the photocatalytic rate constant increases for the best photocatalyst: Cu1-TiO 2 (k obs = 1.2 × 10 2 min −1 ) with the higher surface coverage area (q = 79%).High Cu3-TiO 2 surface coverage decreases the O 2 oxidation (sensitization via visible light) but increases the water's approach to the surface due to a less distribution of Cu3 on the photocatalyst surface.In the low surface coverage area (q = 9%), the UV irradiation was less effective due to the parallel distribution of Cu3, which limited the proximity of water and the formation of hydroxyl radicals.
3.3.2.2,4-Dichlorophenoxyacetic acid.2,4-Dichlorphenoxyacetic acid is a widely used herbicide.It is soluble in water and distributes throughout the body without a specic accumulation.Also, studies are associated with its oncogenicity, genotoxicity, and neurotoxicity.Given all of this, its removal from wastewater is crucial. 184The photooxidation of 2,4dichlorophenoxyacetic acid in aqueous media under UV light exposure using a mesoporous photocatalyst based on the Cu24 (Fig. 26) and 3-aminopropyltrimethoxysilane was studied by Serra and co-workers. 108Aer condensation of tetraethylorthosilicate around a micelle, the hexagonal mesoporous Si-Cu24 was obtained.According to the authors, achieving almost 90% of pesticide degradation aer 30 min in the presence of H 2 O 2 was possible.Aer 6 photocatalytic cycles, 30% of the photocatalytic efficiency was reduced and maintained constant until the tenth cycle.This reduction could be due to the signicant amount of Cu24 leached aer ten cycles.Once again, the Cu24 practically does not leach between the sixth and tenth cycles.
3.3.3.Fenamiphos.Fenamiphos is a nematicide used to control a wide variety of pests.Its toxicity has been studied in aquatic and terrestrial organisms.Its removal by photocatalysis has already been studied. 185Pereira, Azenha and co-workers 85 studied the photodegradation of fenamiphos in aqueous media with Zn5, Zn7, and Zn16 (Fig. 4) immobilized into Al-MCM-41.Aer 300 min under UV light irradiation (l = 320-460 nm), the best photocatalytic rate was obtained with Zn5/Al-MCM-41 (k obs = 8.5 × 10 −3 min −1 for fenamiphos) and the cationic derivative Zn16 (k obs = 8.1 × 10 −3 min −1 for fenamiphos).The cationic material Zn16/Al-MCM-41 could maintain a stable photocatalytic activity aer three reusability cycles.In contrast, when using Zn5/ Al-MCM-41, there was a decrease of 40% in the photodegradation rate aer the same cycles.The authors identied sulfone and sulfoxide (Scheme 1) as the degradation products.

Pharmaceuticals
Antibiotics, anti-inammatory, and anti-depressive drugs are among the thousands of human pharmaceuticals produced and consumed yearly.These drugs reach aquatic habitats via the disposal of domestic sewage.When they reach the wastewater treatment plants, aer some degradation process, they can be converted into other potentially more harmful and long-lasting  Review RSC Advances chemicals. 186Thus, it seems evident that nding innovative and sustainable treatment processes to remove these pollutants from wastewater is essential.In the following sections, the degradation of ibuprofen, naproxen, sulfathiazole, carbamazepine, erythromycin, and tetracycline (Fig. 27) using several phthalocyanines will be mentioned.
3.4.1.Ibuprofen and naproxen.Ibuprofen and naproxen are anti-inammatory drugs widely described.The main source of contamination of these drugs is the excretion of non-metabolized and metabolized drugs in human urine.To avoid the harmful health consequences of ibuprofen and naproxen and its metabolites, removing them from natural water and wastewater is necessary. 187,188To photodegrade ibuprofen and naproxen in aqueous media, Mlynarczyk and co-workers 189 used a material based on Zn4 or Cu4 (Fig. 4) immobilized in TiO 2 .Different photocatalytic activities were obtained depending on the catalyst and type of light used.Both photocatalysts can degrade naproxen more efficiently than ibuprofen.For all the experimental conditions, introducing Zn4 or Cu4 could enhance the photocatalytic activity of bare TiO 2 .When UV irradiation was used, complete degradation of naproxen with Zn4-TiO 2 and Cu4-TiO 2 within 120 min under irradiation.In the case of ibuprofen, more time was needed (360 min) to achieve a 90% degradation using Cu4-TiO 2 and 85% with Zn4-TiO 2 .Under red light irradiation, neither catalyst could degrade ibuprofen.Aer 3 cycles, it was still possible to completely degrade naproxen with Zn4-TiO 2 within 180 min (instead of 120 min in the rst cycle).
3.4.2.Erythromycin.Erythromycin is the rst antibiotic used to treat human infections.Despite most erythromycin and other antibiotics being discharged into the sewage system, reaching wastewater treatment plants, the inadequate disposal of unused medicines also reaches these plants.Their removal from wastewater is essential. 190So, Suganthi, Vignesh, and coworkers 94 studied the degradation of erythromycin in aqueous media under visible light (l > 400 nm) using Zn4 (Fig. 4) with modied TiO 2 nanoparticles (Zn4-TiO 2 ).The composite was prepared by chemical impregnation and used to improve the photocatalytic activity of TiO 2 .According to the authors, the composite has a slightly shied absorption to the visible region of the spectrum and a higher surface area when compared with TiO 2 .As expected, aer 180 min under light irradiation, it was possible to degrade erythromycin using Zn4-TiO 2 (74%) and bare TiO 2 (32%).The photodegradation rate could be maintained aer 5 cycles with the same catalyst.
3.4.3.Tetracycline.Tetracycline is one of the most effective broad-spectrum antibiotics.It gets into the environment through urine and faeces since it is completely absorbed but has a low metabolic transformation.Due to its high stability, it becomes difficult to degrade it under natural conditions.So, it becomes important to nd new, effective, and feasible technologies for the degradation of tetracycline in wastewater. 191Lu and co-workers 80 could photodegrade tetracycline in aqueous media in the presence of Cu5 (Fig. 4)/CeO 2 /Bi 2 MoO 6 nanobers and sunlight.Aer 120 min, it was possible to degrade ∼95% of the tetracycline compared with the material by itself (50%) (without the Cu5).This enhanced photocatalytic activity can be correlated to the synergetic effect between Cu5, CeO 2 , and Bi2MoO 6 .More recently, Li, Guo, and co-workers 81 developed a Fe4/g-C 3 N 4 heterojunction nanosheets for the photodegradation of TC.Aer 40 min of visible light irradiation (l > 420 nm), 97% of TC was degraded.According to the authors, the construction of this heterojunction via p-p conjugation inhibited phthalocyanine aggregation, promoting charge separation and transfer and broadened the response range of visible light.The degradation of TC was extent to wastewater and the degradation rate was maintained.However, the authors did not perform recyclability studies or identify the degradation products of TC.
More recently, Yang, Yu, and co-workers 82 studied the degradation of TC in an aqueous solution under visible light irradiation (l > 420 nm) by using the Fe4 (Fig. 4)/perylene diimide heterojunctions.Aer 60 min of light irradiation, there was degradation of 79% of TC (degradation rate of 0.0264/min).This degradation rate was higher when compared with perylene diimide (41%, 0.0088/min) and Fe4 (2%, 0.0003/min) by itself.Aer ve cycles, the degradation efficiency was almost unchanged.The authors did not study the degradation products of TC.
3.4.4.Carbamazepine.Carbamazepine is an important drug used to treat epilepsy and other psychotherapy applications.This drug is one of the most frequently detected pharmaceuticals in wastewater and their corresponding metabolites. 192So, Lu, Chen, and co-workers 56,109 studied the photooxidation in aqueous media of carbamazepine using PANsupported g-C 3 N 4 coupled with Zn(II) phthalocyanine 2 (Fig. 4) nanobers and an iron hexadecachlorophthalocyanine Fe25 (Fig. 6) coordinated with g-C 3 N 4 previously functionalized with pyridine-based ligand isocotinic acid (INA).According to the rst study, 56 the g-C 3 N 4 /Zn2 was introduced as the catalytic entity, and the PAN nanobers were employed as support to overcome the defects of easy aggregation and enable an easy recycling process.Under solar irradiation, the g-C 3 N 4 /Zn2/PAN could only induce degradation of ∼98% aer 300 min, which could be maintained ve times during the experiment.In the second study, 109 nearly 55% of carbamazepine was degraded over g-C 3 N 4 or g-C 3 N 4 /Fe25 in the presence of Scheme 1 Fenamiphos photooxidation products.peroxymonosulfate within 40 min under visible light irradiation.In the presence of g-C 3 N 4 -INA-Fe25, the removal rate was much higher (∼94%).Almost no degradation was observed without light, even in the presence of peroxymonosulfate.Regarding the degradation products, the authors reported the identication of several intermediates by mass spectrometry in both studies.The degradation products are very similar between the two studies.The difference between them is the utilization of peroxymonosulfate in the second study. 56,109n another study, Anucha, Altin, and co-workers 193 studied the photooxidation of carbamazepine in aqueous media under UV-irradiation using boron/sodium uorine co-doped titanium dioxide sensitized with an axial substituted phthalocyanine Si55 (Fig. 28) (B/NaF-SiHTiO 2 ).Aer 240 min, there was complete degradation using the B/NaF-Si55TiO 2 , whereas the unsensitized B/Na-TiO 2 could only achieve 70% of carbamazepine degradation.Both composites showed higher photocatalytic activity when compared with the bare TiO 2 (40%).In this study, the authors identied similar degradation products to the ones reported by Lu, Chen, and co-workers. 56,109.4.5.Sulfathiazole.The presence of medicines, their metabolites and/or their degradation products, is a current problem. 194The photodegradation of sulfathiazole in aqueous media under visible light irradiation (l > 400 nm) was studied by Yang and co-workers. 195They used well-faceted TiO 2 nanosheets with coexposed (001) and ( 101) and deposited selectively on a-Fe 2 O 3 and Fe/Co-N 4 on (001) facets (NTiO 2 -NS).Then, they prepared a hybrid material containing NTiO 2 -NS and Co3 (Fig. 4).There was 65% sulfathiazole degradation with the prepared catalyst, which was much higher when compared to NTiO 2 -NS (20%).Also, even aer 40 recycle usages, the photocatalytic performance had no signicant changes.

Other pollutants
Other pollutants such as trichlorobenzene (TCB), aniline, and dimethyl phthalate were found in wastewater.These aromatic compounds are considered toxic and should be eliminated from wastewater. 83,99,196In the following three studies, the authors analysed the degradation of these pollutants by using two different phthalocyanines.
3.5.1.Chlorobenzene and 1,2,4-trichlorobenzene.Gül and co-workers 99 evaluated the photocatalytic degradation of chlorobenzene (PhCl) and TCB using TiO 2 sensitized with Co15 and Zn15 (Fig. 4) under visible light (l > 400 nm).Compared with the previous study, the Co15 and Zn15 could also remove PhCl and TCB within 30 min under visible light irradiation.The recyclability studies showed no more than 16% loss aer 5 cycles (Table 12).3.5.2.Aniline.The photodegradation of aniline in aqueous media under visible light using chitosan-H 2 4-TiO 2 (Fig. 4) hybrid was accessed by Bouattour and co-workers. 196In the presence of unmodied samples, there was a 30% degradation of aniline within 600 min.Aer sensitization with H 2 4, two different hybrids were obtained according to the amount of phthalocyanine: A-H 2 4/ chitosan-TiO 2 (1 wt%) and B-H 2 4/chitosan-TiO 2 (2 wt%).Under visible light irradiation, the A-H 2 4/chitosan-TiO 2 and B-H 2 4/chitosan-TiO 2 have higher photocatalytic activity when compared with the unsensitized hybrid and bare TiO 2 .Aer 10 h, it was possible to degrade ∼70% and 50% of aniline using A-H 2 4/chitosan-TiO 2 and B-H 2 4/chitosan-TiO 2 , respectively.The second catalyst could be reused up to three times, with a loss of 20% on their photocatalytic activity.This loss was mainly observed from the rst to the second cycle (16%).

Summary and outlook
This review shows the signicant advances for the photocatalytic degradation of several water pollutants using simple Pc derivatives or Pcs immobilized on organic or inorganic materials, such as polymers, bres, carbon nanostructures, ZnO, SiO 2 , TiO 2 , or mixtures of these supports, when exposed to UV, visible, UVvisible, and/or solar light irradiation.It is also shown that the photocatalytic activities of the phthalocyanine dyes are strongly correlated with their substituents, the presence/absence of positive charges, and the metal ions on their macrocycle structure.
The light source (UV, UV-visible, visible, or solar) is also a key element for the photodegradation approach.When solar/visible light is used, the Pc can be excited along with the support, but only a small or no excitation of the Pcs is observed using UV light.The use of solar light is considered an enormous advantage for photocatalysis since it reduces costs and takes advantage of the solar spectrum.It is also important to mention that most photocatalytic studies lack reusability studies, an essential parameter for the potential industry application.However, for most of the reused catalysts, no signicant loss of activity was observed, and, in some cases, the photocatalyst is specic for a selected pollutant.
This review highlights the efforts of the scientic community to nd new alternative methodologies for the degradation of pollutants, which are usually difficult to remove from water.The most critical issue is the prevention of Pcs leaching, which was revealed to be the leading cause of activity loss of the photocatalysts aer several cycles of their use.Almost all the works mentioned in this review referred to the recyclability of the photocatalysts.Fortunately, the tendency to carry out those studies has been increasing over time.Moreover, for a scientist who wants to reproduce the reported work, it is important to know the exact conditions of the photocatalytic assay, namely the irradiance of the lamp used.However, most of the cited papers in this review did not mention the irradiance of the lamp used (nor the lamp's brand), making it difficult to compare results and even reproduce them.Nevertheless, the application of these photocatalysts in wastewater is (urgently) needed to offer an important insight for addressing future environmental challenges.

Literature review information
The search for research papers for this review was conducted in 2021, but it was updated in April 2023 before the submission of the manuscript.This review has 103 papers on photocatalytic studies and a total of 196 references dated from 2007 to 2023.

Fig. 1
Fig. 1 Condensed and simplified structural chemical formulae used for phthalocyanine having an aor b-substitution patterns.

Fig. 2
Fig. 2 Proposed mechanism for the Pc mediated photodegradation of wastewater pollutants under visible light irradiation.

Fig. 10
Fig.10Structure of the main five groups of organic dyes described in this review.

Fig. 12
Fig. 12 Zn40-Zn42 coupled to CoFe 2 O 4 MNP used by Nyokong and co-workers 142,143 for the degradation of MO.

Fig. 13
Fig. 13 In(III)18Cl or Zn(II)18 covalently bonded to MNP of Fe 3 O 4 or Gd 2 O 3 used by Nyokong and co-workers 103 for the degradation of MR.

Fig. 19
Fig. 19 Perylene diimide derivative used by Zhang and co-workers 166 for conjugation with Cu47 and used for the degradation of RhB.

Fig. 20
Fig. 20 First intermediates in the degradation of RhB resulted from the cleavage of ethyl groups.

Fig. 22
Fig. 22 Hollow Fe 3 O 4 @SiO 2 @TiO 2 nanostructure sensitized with Co3 used by Liu and co-workers 177 for the degradation of MB.

Fig. 25
Fig.25Structure of the agrochemicals mentioned in this review.

Fig. 27
Fig. 27 Pharmaceuticals for photodegradation studies mentioned in this review.

Table 3
Photophysical parameters for the degradation of 4-CP under visible light irradiation (l > 400 nm)

Table 5
Photophysical parameters for the degradation of 2,4-DCP

Table 6
Comparison of the photocatalytic degradation of PCP using different Pcs © 2023 The Author(s).Published by the Royal Society of Chemistry RSC Adv., 2023, 13, 33957-33993 | 33969

Table 7
Photophysical parameters for the degradation of MO

Table 8
86otocatalytic efficiencies of Cu3, Cu4, and Cu25 immobilized on TiO 2 .86MohamedandYoussef 157sed a nickel(II) phthalocyanine Ni44 (Fig.15) immobilized on TiO 2 nanoparticles and visible light irradiation (l > 400 nm).The characterization of the resulting material showed that Ni44 is anchored to the surface of TiO 2 through SO 2 -O-TiO 2 bonds.It was possible to achieve complete degradation of BPB within 50 min.No signicant loss of activity was observed aer 3 cycles.3.2.2.3.Brilliant blue (acid blue 9) and fuchsine (basic violet Fig. 15 Phthalocyanine 44 used by Mohamed, Youssef and coworkers 155,157 for the degradation of CV and BPB.© 2023 The Author(s).Published by the Royal Society of Chemistry RSC Adv., 2023, 13, 33957-33993 | 33975

Table 10
Photocatalytic parameters for the degradation of RhB a With 0.25 mg of photocatalyst amount.© 2023 The Author(s).Published by the Royal Society of Chemistry RSC Adv., 2023, 13, 33957-33993 | 33977

Table 11
Photophysical parameters of Pcs immobilized on several supports used for the photocatalytic activity of MB a Amount of silicate polymer network.